Packet Generator

This tool
allows you to edit and send packets via your network card. To open
the Packet Generator, clickTools
=> Packet Generator, or select a packet from
thePacketstab,
right-click on it, and select theSend
Packetcommand.

Please note
that the Packet Generator cannot and should not be used for sending
application-layer TCP streams, i.e. it cannot take care of
incrementing SEQ or ACK values automatically, adjusting checksums
and packet sizes and so forth. If you need to send a TCP stream,
you should use a Winsock-based application specifically designed
for that purpose. The Packet Generator is a tool for replaying
pre-captured data, testing firewalls and intrusion detection
systems, as well as for performing other specific tasks that
require manual packet crafting.

The Packet
Generator allows you to change the packet contents and have the
packet decode displayed in the left window as you edit it. You can
create packets of any kind; you have full control over the packet
contents. For IP, TCP, UDP, and ICMP packets, you can automatically
correct the checksum(s) by clicking on theSigmabutton. To
assist you with packet editing, theVisual Packet
Buildertool is also
available; click on the
corresponding button to invoke it.

You can also
click on the button with an arrow on it to display the list of
available packet templates. The program comes withTCP,UDP,
andICMPpacket
templates; using them is often faster than typing hex codes in the
editor window. These templates contain typical TCP, UDP, and ICMP
packets, but you would most probably want to edit many packet
fields and use meaningful values that suit your needs, such as real
MAC and IP addresses, port numbers, SEQ and ACK numbers, etc. You
can use your own templates rather than the built-in ones. You can
drag-and-drop a packet from the CommView Packets tab to the
Templates section in the Packet Generator window. If you drop
several packets into the Templates section, only the first packet
will be used as a template. An entry named New Template will appear
in the list of templates. You can rename a template by
right-clicking on it in the list and selectingRename.
If you need to delete a template, right-click on it and
selectDeletefrom the
pop-up menu. Selecting a template in the list will load the packet
that it contains in the editor window where it can be edited prior
to sending.

You can also
place NCF files with the templates of your choice to the TEMPLATES
subfolder in the application folder. If CommView finds NCF files
(or just one of them) in the TEMPLATES subfolder, it will list them
among the available templates in the drop-down list. These NCF
files should contain only one packet per file, but if you use a
file that contains many packets, CommView will load only the first
one.

Once you have
edited a packet, use the controls below to send it:

Packet
Size–
modifies the packet size.

Packets
Per Second– controls the speed at
which packets will be sent. Be sure not to send packets too fast if
you have a slow connection. For example, sending a 1,000 byte
packet 5,000 times per second is more than your 10Mbit NIC can
handle.

Continuously– select this
option if you want the Packet Generator to send packets
continuously until you click Stop.

Time(s)– select this
option if you want the Packet Generator to send packet a given
number of times.

Send/Stop– click this
button when you are ready to send packets or to stop sending
them.

Working with multiple packets

You can use
the Packet Generator to send multiple packets at once. To do that,
just select the packets you want to send in the list and invoke the
Packet Generator using the right-click menu, or drag and drop the
selected packets to the Packet Generator window. Alternatively, you
can drag and drop capture files in all supported formats directly
to the Packet Generator window. When multiple packets are being
sent, the packer editor and decoder tree become invisible.

Saving edited packets

If you edit a
packet and would like to save it, just drag the decoder tree to the
desktop or any folder, and a new file in NCF format containing the
packet will be created. The file name is always PACKET.NCF. You can
also drag the packet to the templates window. If you need to edit
and send multiple packets, edit them one by one, each time dragging
a new packet to the desktop and renaming it. After that, open a new
Log Viewer window, drag-n-drop the edited packets from the desktop
to Log Viewer, select them using the Shift button, and invoke the
Packet Generator using the context menu.

WARNING:

1.

Don't use
the Packet Generator unless you know exactly what effect you want
to achieve. Sending packets may produce unpredictable results, and
we strongly recommend refraining from using this tool unless you
are an experienced network administrator.

2.

There
should be at least one working computer on your LAN besides your
own computer when you use this tool. Otherwise, you will experience
severe delays in sending packets.